1. Field of the Invention
This invention concerns a porous fibrous structure and, more in particular, it relates to a novel porous fibrous structure having a plurality of indefinite cellular cavities inside the fibrous structure and a manufacturing method thereof.
2. Description of the Prior Art
Products prepared by bonding non-woven fabrics or block form fibrous structures with adhesives or adhesive fibers have been generally used. Various proposals have been made to use such products where an application requires bulkiness. For example, a method of impregnating a fibrous structure with a foaming agent to provide bulkiness by foaming of the agent and a method of dissolving water soluble fibers out of the fibrous structure containing the water soluble fibers thereby providing bulkiness have been proposed. Although such prior art techniques provide bulkiness to some extent to the fibrous structure, their effect is extremely small.
Further, in the former method, since the fibers are embedded in the foamed resin, property inherent to the fibers such as softness and hygroscopic property can not be developed. In the latter method, the size of the cavity formed between the fibers is not larger than the space occupied by the fibers removed by dissolution and, as a result, the porosity is restricted and the utilization factor of the fibers is reduced since the starting fibers are partially removed by dissolution.
Further, Japanese Published Unexamined Patent Application Sho 59-76959 and Sho 60-28565 disclose non-woven fabrics obtained by mixing polypropylene fibers formed by incorporating azodicarboxylic acid amide as a blowing agent into the surface of the fibers thereby forming a plurality of fine cleft holes to the surface with binder fibers and applying heat treatment. However, the non-woven fabric obtained by this method has no cellular cavities in the non-woven fabric but this method tends to modify the surface smoothness of the synthetic fibers by the presence of fine cleft holes on the surface of the fibers. On the other hand, wadding is applied as filling fibers or core materials to mattresses and stuffed dolls but all of them have uniform structure in which wadding is entangled at random and have no cellular cavities.
Fibrous structures consisting only of fibers and with extremely high porosity having indefinite cellular cavities have not yet been known.